Hi guys not sure how to approach these questions would appreciate being pointed in the right direction :)

Question:

Expand the following expressions, collecting together like terms where possible;

1. (ax + b) ^2

2. 4(x/2 - 3 ) (7y - x)

Thanks in advance :)

May 11th 2011, 12:21 PM

DrSteve

1. To square an expression means to multiply that expression by itself. So this is equal to (ax+b)(ax+b). Can you FOIL this expression?

2. Leave the 4 outside, and FOIL the two binomials. Give it a shot and let's see how you do.

May 11th 2011, 12:36 PM

komodo

Quote:

Originally Posted by DrSteve

1. To square an expression means to multiply that expression by itself. So this is equal to (ax+b)(ax+b). Can you FOIL this expression?

2. Leave the 4 outside, and FOIL the two binomials. Give it a shot and let's see how you do.

Thanks for the quick response Steve :)

I'm not familliar with the term FOIL are you possibly refering to multiplying the brackets out?

Thanks :)

May 11th 2011, 01:20 PM

scounged

Quote:

Originally Posted by komodo

Thanks for the quick response Steve :)

I'm not familliar with the term FOIL are you possibly refering to multiplying the brackets out?

Thanks :)

Yes. FOIL is a mnemonic i think it's called. Multiplying the brackets out is the same thing as expanding an expression, so do that.

May 11th 2011, 02:25 PM

komodo

I think I understand that I have multiply the First, Outter, Inner and Last in that order then collect like terms hence FOIL.

Can someone give me the answers so I can check if I've done it correctly :)

Thanks guys :)

May 11th 2011, 02:42 PM

Quacky

Quote:

Originally Posted by komodo

I think I understand that I have multiply the First, Outter, Inner and Last in that order then collect like terms hence FOIL.

Can someone give me the answers so I can check if I've done it correctly :)

Thanks guys :)

Post your answers, and we'll tell you if you're correct.

May 11th 2011, 04:02 PM

komodo

Quote:

Originally Posted by Quacky

Post your answers, and we'll tell you if you're correct.

This is what I got for the 1st one not sure if I've done it correctly though....

(ax + b) ^2

= (ax + b) (ax + b)

= (2ax + axb) (axb + b^2)

= 2ax + 2axb + b^2

Is this correct feels like I've done something wrong :(

May 11th 2011, 04:14 PM

Quacky

Quote:

Originally Posted by komodo

This is what I got for the 1st one not sure if I've done it correctly though....

(ax + b) ^2

= (ax + b) (ax + b)

= (2ax + axb) (axb + b^2)

= 2ax + 2axb + b^2

Is this correct feels like I've done something wrong :(

Just some silly errors. If I have then this is (because the order of multiplication doesn't matter) which is the same as So this is the change you need to make:

(don't use brackets for addition!)

Otherwise, it's fine. Be careful with how you set your work out, try and follow my example above for the second problem, and just be cautious where you put brackets (implying multiplication) and plus signs (obviously for addition).

May 11th 2011, 05:05 PM

komodo

Quote:

Originally Posted by Quacky

Just some silly errors. If I have then this is (because the order of multiplication doesn't matter) which is the same as So this is the change you need to make:

(don't use brackets for addition!)

Thanks for the advice it was a pretty stupid mistake....the 2nd expression is also proving kind of tricky its different to all the previous exercises that I've attempted prior but here is a long shot at it:

4 (x/2 - 3) (7y - x)

= 4 (x/2.7y - x^2/2 - 21y - 3x)

Dont know whether to multiply everything in the brackets by the 4 outside or even if whats in the brackets is correct...help would be much appreciated :)

May 11th 2011, 05:07 PM

Quacky

Quote:

Originally Posted by komodo

Thanks for the advice it was a pretty stupid mistake....the 2nd expression is also proving kind of tricky its different to all the previous exercises that I've attempted prior but here is a long shot at it:

4 (x/2 - 3) (7y - x)

= 4 (x/2.7y - x^2/2 - 21y - 3x)

Dont know whether to multiply everything in the brackets by the 4 outside or even if whats in the brackets is correct...help would be much appreciated :)

Yeah, you want to multiply everything inside by 4. You've made a slight sign error: